The present invention is directed to a method of rehabilitating and stabilizing salt contaminated concrete structures.
It is well known that reinforced concrete structures, such as bridges, parking garages, and the like are highly susceptible to corrosion and degradation from commonly applied chloride deicing salts. It is believed that a large percentage of all bridge decks in the United States and in other countries which have cold climates are seriously deteriorated because of corrosion of the reinforcing steel which is part of their structure. This corrosion is usually caused by chloride ions that have penetrated the concrete as a result of repeated application of deicing salts. In the case of concrete parking structures, automobiles carry salt contaminated ice and snow to the structure and, while parked, allow the contaminated ice and snow to melt and concentrate on concrete structure. In all cases accumulation of corrosion products around the reinforcing steel causes cracks to develop in the concrete cover. This allows even more rapid intrusion of additional chloride solution and, thereby, accelerates corrosion and spalling of the concrete structure. If corrosion and spalling is allowed to continue, the metal reinforcements, as well as the surrounding concrete, deteriorate to a point which requires substantial removal and replacement of the entire structure. This is a difficult and costly endeavor.
Several methods have been suggested to ameliorate the condition of concrete structures which have undergone or are susceptible to corrosion deterioration. For example, low permeability overlays have been applied to deteriorated structures. In such instances, spot repairs of severely deteriorated concrete is first accomplished. However, large areas of chloride-contaminated concrete remain in place and, although slowed, corrosion and deterioration continue to occur. Thus, this method alone does not address the need for a long-term rehabilitation procedure.
A rehabilitation technique which is often used involves scarifying the top portion of a bridge deck or the like prior to application of a new overlay. Scarification to a level within 0.5 inch of the embedded reinforcement metal elements removes a major amount of contaminated concrete, permits impregnation of corrosion inhibiting agents to the concrete around the steel reinforcements and then application of a new overlay concrete structure. A preferred mode requires removal of the concrete surrounding the steel reinforcements prior to applying a new overlay. These methods are not cost-effective and are, therefore, only viewed as a secondary means to the complete removal and replacement of the concrete structure.
In an attempt to offer a more cost effective method to nullify the effects of chlorides and other corrosion elements to concrete structures and to cause the resultant structure to exhibit long-term effectiveness, impregnation of salt-contaminated, but structurally sound structures, with corrosion resisting materials has been proposed. Impregnation to a depth sufficient to encapsulate the reinforcement was thought to provide the long term protection. Impregnation with polymers such as methyl methacrylate, or water tolerant monomers and/or corrosion inhibitors, have been attempted but have been found to be costly, difficult to apply and have detrimental effects with respect to the resultant concrete properties.
Prior impregnation techniques have been found difficult to carry out in an effective manner. It is well known that concrete is a porous structure. The pores contain residual water from that used during hydration of the cement as well as rain water and the like which has penetrated into the pores over a period of time. Thus, impregnation of organics or even aqueous solutions into such already occupied pores has been found to be extremely difficult. It has been previously proposed that impregnation be carried out by first heating the concrete structure to drive-off the water contained in the pores followed by application of the impregnating solution. However, when this method has been previously used the resultant structure showed extensive cracking which not only weakened the structure but also made it more susceptible to attack by subsequently applied chloride salts.
There is the need for a process which can provide a feasible and effective means of arresting corrosion of reinforcement in sound but corrosive salt-contaminated concrete without causing detrimental effects to the other desired concrete properties such as strength, permeability freeze/thaw properties and structural soundness. Further, there is a need to provide a process of posttreating a sound concrete structure to insure its ability to withstand the corrosive forces of subsequently applied corrosive causing agents, such as chloride salts.